This invention relates to inorganic scintillators and processes for making such scintillators.
Scintillators are devices which, under charged particle or radiation bombardment, will produce visible luminescence and may be employed in applications involving the detection and/or imaging of charged particles. Such applications include cathode ray tubes and screens for electron microscopy, for example.
Scintillator media are usually thick, single crystals (of sodium iodide, calcium fluoride, cesium iodide, for example), powder dispersions, or organic films.
A limitation of single crystal scintillators is that they are too thick for certain applications. For example, since the thickness of single crystals is usually greater than the stopping distance of the charged particles, the resultant luminescence efficiency is reduced due to strong self-absorption of their own luminescence. They also exhibit poor resolution for imaging applications due to light dispersion in the thick layer. Another difficulty is that these single crystals are usually hygroscopic and absorb water which rapidly degrades their efficiency.
A limitation of powder scintillators is that they exhibit poor resolution for imaging; and, because of the powder dispersion, they exhibit very poor mechanical stability. Due to the particulate nature of powder scintillators the absorption of electrons or other charged particles is poor, which results in decreased efficiency. In addition the generated light scatters because of the particles. Thus, powder scintillators must be very thin and this acerbates the problem of mechanical stability. Another limitation of powder scintillators is that their luminescence output is not linear with increasing particle current density; this is due to their inability to readily dissipate heat produced under bombardment resulting in thermal quenching of the luminescence output.
Organic scintillators are limited in that they suffer from rapid performance degradation, due to radiation damage. Organic scintillators can be provided as thin films and have very rapid response times, but unfortunately have short lives.